Cooled antenna feed for a telescope array

Abstract

An offset Gregorian antenna used in radio astronomy. The antenna may include a primary reflector having a substantially paraboloidal shape and a secondary reflector having substantially an ellipsoidal shape. The secondary reflector may be displaced from the optical axis of the primary reflector. The antenna may also include a feed located substantially coincident with the second focus of the secondary reflector. The feed may be located within a vacuum sealed enclosure, and a cryo pump may be used to cool the feed within the enclosure. Also, a shroud may partially surrounding the feed.

What is claimed: 
     
         1 . An offset Gregorian antenna, comprising:
 a primary reflector having a substantially paraboloidal shape;   a secondary reflector having substantially an ellipsoidal shape, displaced from the optical axis of the primary reflector;   a feed located substantially coincident with the second focus of the secondary reflector;   a cryo pump to cool the feed; and   a shroud partially surrounding the feed.   
     
     
         2 . The antenna of  claim 1 , wherein the first focus of said secondary reflector is substantially coincident with the focus of the primary reflector 
     
     
         3 . The antenna of  claim 1 , wherein the shroud is located between the feed and a ground while providing substantially unimpeded passage of radiation between the feed and the primary reflector and the secondary reflector. 
     
     
         4 . The antenna of  claim 1 , wherein the primary reflector has a diameter of about 6 meters. 
     
     
         5 . The antenna of  claim 1 , wherein the secondary reflector has a diameter of about 2 meters. 
     
     
         6 . The antenna of  claim 1 , further comprising an enclosure surrounding the feed. 
     
     
         7 . The antenna of  claim 6 , wherein the enclosure is vacuumed sealed. 
     
     
         8 . The antenna of  claim 6 , further comprising a polyethylene anti-reflective material covers a portion of the enclosure. 
     
     
         9 . The antenna of  claim 6 , wherein the enclosure is made of borosilicate glass. 
     
     
         10 . The antenna of  claim 6 , wherein the enclosure is made of fused quartz. 
     
     
         11 . The antenna of  claim 6 , wherein the enclosure is made of composite materials. 
     
     
         12 . The antenna of  claim 1 , wherein the feed includes a low noise amplifier. 
     
     
         13 . The antenna of  claim 12 , wherein the low noise amplifier includes a chassis, an input coax cable connected to one end of the chassis and an output coax cable connected to an opposite end of the chassis. 
     
     
         14 . The antenna of  claim 13 , wherein the resistance of the input coax cable is about 95 ohm. 
     
     
         15 . The antenna of  claim 13 , wherein the resistance of the output coax cable is about 50 ohm. 
     
     
         16 . The antenna of  claim 12 , wherein the low noise amplifier is disposed at a tip of the feed. 
     
     
         17 . The antenna of  claim 1 , wherein the feed includes a thin rexolite standoff 
     
     
         18 . The antenna of  claim 1 , further comprising a vibration isolation mechanism connected to the feed to dampen vibrations. 
     
     
         19 . An offset Gregorian antenna, comprising:
 a primary reflector having a substantially paraboloidal shape;   a secondary reflector having substantially an ellipsoidal shape, displaced from the optical axis of the primary reflector;   a feed located substantially coincident with the second focus of the secondary reflector;   a vacuum sealed enclosure surrounding the feed; and   a cryo pump in communication with the vacuum sealed enclosure to cool the feed within the vacuum sealed enclosure.   
     
     
         20 . The antenna of  claim 19 , wherein the cryo pump cools the feed within the vacuum sealed enclosure to less than 65 K.